The problem with attack speed
First things first, lets get this out of the way, kog ma's attack speed nerf did not fix or help the situation in any way it only made it take longer for him to reach the point that her becomes a Gatling gun..
Now that we got that of the way let me tell you what really is the issue here: Attack speed items. There are way too many of them now, not to try to incentivize this plan of building all of them. The only problem is that I'm not sure what makes building all attack speed items a negative verses building all ap items or all ad items. my only guess is that shooting extremely fast should in theory mean there's no damage but when the items still give ad or when the speed at which you're shooting is so fast that the time it takes to equal the amount of damage done if you build pure ad is greater then the ad build then something is wrong (maybe?).
But no matter what the issue is there should be a solution for it right? maybe it's frozen + thorn-mail? or maybe it's an issue with the items. Personally i want to suggest an idea for balancing the items. ultimately it's up to you.
If you are to assume with me that the items are the problem then hear me out on this idea. Limit the amount of attack speed items you can buy, just like how gold or jungle items are, i honestly think there should be a limit but i cant decide what it should be. (I'm thinking 1-3). The reason i think this is because if practically anyone can make the build and have it work for them, then forcing champions to only pick a few will stop the abuse in it's tracks. Again thou i enjoy to hear your thoughts on this. as for now I'll continue to enforce a 100% ban on kog ma